MacViews: draw combobox arrow backgrounds

ui/native_theme/native_theme_mac.mm

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/native_theme/native_theme_mac.h"
 
 #import <Cocoa/Cocoa.h>
 #include <stddef.h>
 
 #include "base/mac/mac_util.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/mac/sdk_forward_declarations.h"
 #include "base/macros.h"
 #import "skia/ext/skia_utils_mac.h"
+#include "third_party/skia/include/core/SkRRect.h"
 #include "third_party/skia/include/effects/SkGradientShader.h"
+#include "ui/gfx/color_palette.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/skia_util.h"
 #include "ui/native_theme/common_theme.h"
 
 namespace {
 
 // Values calculated by reading pixels and solving simultaneous equations
 // derived from "A over B" alpha compositing. Steps: Sample the semi-transparent
 // pixel over two backgrounds; P1, P2 over backgrounds B1, B2. Use the color
 // value between 0.0 and 1.0 (i.e. divide by 255.0). Then,
@@ skipping 233 matching lines @@
       // and is a good shade of gray, it's not blue enough for the Blue theme.
       paint.setColor(GetSystemColor(kColorId_HoverMenuItemBackgroundColor));
       canvas->drawRect(gfx::RectToSkRect(rect), paint);
       break;
     default:
       NOTREACHED();
       break;
   }
 }
 
+skia::RefPtr<SkShader> NativeThemeMac::GetButtonBackgroundShader(
+    NativeTheme::State state, int height) const {
+  typedef SkColor ColorByState[NativeTheme::State::kNumStates];

[tapted, 2016/03/22 11:20:26]

nit: typedef const? or const below for start/end colors

[Elly Fong-Jones, 2016/03/22 22:05:10]

Acknowledged.

+  SkPoint gradient_points[2];
+  gradient_points[0].iset(0, 0);
+  gradient_points[1].iset(0, height);
+
+  // TODO(ellyjones): These colors are not exactly right, and the gradient
+  // probably needs more stops.
+  SkScalar gradient_positions[] = { 0.0, 0.38, 1.0 };
+
+  // TODO(ellyjones): Does this need to handle states other than kHovered and
+  // kNormal?

[tapted, 2016/03/22 11:20:26]

I think this can be removed, or replaced with a comment like, 

// Order is Disabled, Hovered, Normal, Pressed.

Although it's annoying this is a different order to views::Button::ButtonState
(normal, hovered, pressed, disabled). It takes up 5 lines anyway, so we could do

start_colors[...DISABLED] = ...
start_colors[...HOVERED] = ...

(compilers are smart these days right?)

[Elly Fong-Jones, 2016/03/22 22:05:10]

I can only do this by stripping off the const, since default initialization of
const variables isn't allowed and C++ does not have designated initializers, but
I like it more than the other thing, so away the const goes.

+  ColorByState start_colors = { gfx::kMaterialGrey300,
+                                gfx::kMaterialBlue300,

[tapted, 2016/03/22 11:20:26]

I'm pretty sure we don't want hover states - this should be the same as 'Normal'

[Elly Fong-Jones, 2016/03/22 22:05:10]

Done.

+                                SK_ColorWHITE,
+                                gfx::kMaterialBlue300
+  };
+  ColorByState end_colors = { gfx::kMaterialGrey300,
+                              gfx::kMaterialBlue700,
+                              SK_ColorWHITE,
+                              gfx::kMaterialBlue700
+  };
+
+  SkColor gradient_colors[] = {
+    start_colors[state], start_colors[state], end_colors[state]
+  };
+
+  skia::RefPtr<SkShader> gradient_shader = skia::AdoptRef(
+      SkGradientShader::CreateLinear(
+          gradient_points, gradient_colors, gradient_positions, 3,
+          SkShader::kClamp_TileMode));
+  return gradient_shader;
+}
+
+void NativeThemeMac::PaintComboboxArrowBackground(SkCanvas* canvas,
+                                                  State state,
+                                                  const gfx::Rect& rect) const {
+  // TODO(ellyjones): This constant is duplicated in FocusableRoundedBorder at
+  // the moment. Maybe this function should take this as a parameter instead.
+  const int kComboboxBorderRadius = 5;

[tapted, 2016/03/22 11:20:26]

I think we want a constant in native_theme_mac.h or platform_style[_mac].h,
since it's needed for other controls too.

[Elly Fong-Jones, 2016/03/22 22:05:10]

Done.

+
+  // The combobox arrow is a logical button, so it has a button background
+  // gradient.
+  skia::RefPtr<SkShader> shader =
+      GetButtonBackgroundShader(state, rect.height());
+
+  SkPaint paint;
+  paint.setShader(shader.get());
+  paint.setStyle(SkPaint::kFill_Style);
+  paint.setAntiAlias(true);
+
+  SkPoint no_curve = SkPoint::Make(0, 0);
+  SkPoint curve = SkPoint::Make(kComboboxBorderRadius, kComboboxBorderRadius);
+  // Curve upper-right and lower-right corners of the background only.
+  SkVector curves[4] = { no_curve, curve, curve, no_curve };
+
+  SkRRect fill_rect;
+  fill_rect.setRectRadii(gfx::RectToSkRect(rect), curves);
+
+  canvas->drawRRect(fill_rect, paint);
+}
+
 NativeThemeMac::NativeThemeMac() {
 }
 
 NativeThemeMac::~NativeThemeMac() {
 }
 
 }  // namespace ui